The present invention relates to optical imaging. More particularly, the present invention relates to capturing images of moving objects by moving the point source of illumination generally synchronously with the motion of the object to prevent or minimize blurring of the captured images while, at the same time, increasing the throughput of the imaging process.
In the field of high-speed industrial imaging, it is desirable to maintain objects in motion at constant velocity in order to maximize the throughput of the production line. Imaging techniques in which imaging is performed by transmission of illumination through an object to a detector, such as in x-ray radiography, are commonly referred to as projection imaging techniques. The images captured during imaging are referred to as projection images. The general problem of imaging an object in motion is a result of the time of the exposure and the apparent motion in the focal plane. In general, if an object travels in one dimension at some velocity VO during a time, Δt, which corresponds to the exposure time, then the image will be blurred with an effective resolution of VO*Δt.
For many situations, if the exposure time is sufficiently short or if the velocity of the object is sufficiently small, an imaging system can perform the required task of imaging the moving object without unacceptable blurring. However, there are a number of cases where shortening the exposure time or reducing the velocity of the object are not adequate solutions to the problem of blurring, particularly in industrial imaging. For example, in many situations the object velocity may be fixed, or the intensity of the illumination provided by the illumination source may be insufficient to allow short exposure times to be used. In addition, the exposure time may be constrained for some reason. Also, there may be a need to move the object at a speed beyond that at which an acceptable amount of blurring could be obtained.
Another way to avoid or minimize blurring is to stop the motion of the object each time an image of the object is to be captured and capture an image, move the object to the next imaging position, stop the object and capture an image of the object at that position, and so on, as the object is moved along the manufacturing line. However, in many situations, it is highly undesirable to start and stop the object during imaging. Starting and stopping the object during imaging generally results in substantial imaging complexity and delay time because the imaging system must wait for the object to settle into each new position in order to image the object with sufficient precision and to avoid blurring. Also, the delay time associated with stopping and starting the object decreases the throughput of the imaging system.
Accordingly, a need exists for an imaging system that can obtain precise images of an object while the object is in motion while minimizing blurring, thereby maximizing imaging throughput.